[beisik]

Я делаю так:

var
  fps_time: integer;
  fps_cur: integer;
  fps: integer;

...

procedure CountFPS;
begin
  if fps_time <= GetRelativeTimeMs then
  begin
    fps_time := GetRelativeTimeMs + 1000;
    fps := fps_cur;
    fps_cur := 0;
  end;
  fps_cur := fps_cur + 1;
end;

...

// Инициализация:
 fps_time := GetRelativeTimeMs - 1000;

...

// При каждой отрисовке
  CountFPS;

...

// Выводим
  DrawText('FPS: ' + IntegerToString(fps), 8, 8);